Bob Newhart visits ‘The Big Bang Theory’

The 83-year-old isn’t planning a full stop anytime soon.

Sheldon played by Jim Parsons, right, and Leonard hire Professor Proton, played by guest star Bob Newhart, left, the host of their favorite childhood TV show, to perform, on "The Big Bang Theory," Thursday, May 2 on the CBS Television Network.

You can see it in his appearance Thursday night on CBS’ “The Big Bang Theory,” where he’s “Professor Proton,” the hilariously bemused childhood idol of Sheldon (Jim Parsons) and Leonard (Johnny Galecki). You can also see it in the sitcom legend’s willingness to hold out for just the right opportunity.

“Chuck (Lorre, the show’s co-creator) and I have been talking about this for a long time, and we (could) never agree on the show,” said Newhart in a recent phone interview.

“I wasn’t a big fan of (Lorre’s) ‘Two and a Half Men,’ but I am a big fan of ‘The Big Bang Theory,’ and I thought it was extremely well-written and it’s done in front of a live audience, and those were the two requirements that I had.”

Actually, he had a third – he wanted to return for at least two more episodes, something he hopes will happen next season.

“It’s a little more important than a guest shot,” said the former “Newhart” star, who’s also appeared in “NCIS” and ABC’s “Desperate Housewives,” and whose dramatic arc on “ER” scored an Emmy nomination.

(That Newhart’s never actually won an Emmy – for comedy or drama – is reason enough not to take awards too seriously.)

He may have made an art form of the well-placed pause – or stammer – but the 83-year-old Newhart isn’t planning a full stop anytime soon.

“This year, I’ll do 20, 25 appearances – one-night appearances,” he said. “I couldn’t imagine not doing (it). First of all, it keeps your mind fresh and fertile. And to not have something to look forward to, it would drive me nuts. I’ve said in the past that the alternative is like ‘Sunset Boulevard,’ where you just sit in a darkened room and watch old episodes of ‘The Bob Newhart Show.’”

He and Don Rickles – who will be 87 on May 8 – are “doing an interesting thing in Vegas at the end of May,” at an AARP convention, Newhart said.

“Don and I are going to be on stage, not doing our individual acts, but just talking about the trips we’ve taken and the laughs we’ve had and then open it up to Q&A,” he said. (The two comedians and their wives have long vacationed together.)

They’ll be the ones who aren’t retired.

“I take a certain enjoyment out of when you play some of these retirement (places). … I’m hoping there’s a message that, ‘Look, I’m 83, and it’s not over, you know. It’s strictly in your mind.’”

There are lessons from Newhart’s career for people much younger.

The former Chicago accountant got his start in comedy recording funny phone calls with a friend at an advertising agency, eventually getting them on local radio, a route not that different from the podcasts that comedians use today to get their material heard.

Newhart did it, he said, “to keep from going crazy,” but it also honed his skills for an eventual move into stand-up.

“I was the writer and so I had to write something every day,” he said. “And so I had that discipline of coming up with something. And then at one point, Ed (Gallagher), my partner, he got pneumonia, and we were really close to being in violation of our contract (with the radio stations carrying their act). They didn’t have to pay us. So we had to do 10 shows in one night. And we snuck into this recording studio and we recorded and that’s when we just improvised.

“Then Ed, he got a better job in New York, and so then that’s when I started working as a single.”